From: Wally Plumley [wplumley@bellsouth.net]
Sent: Sunday, November 18, 2001 9:57 AM
To: 928
Subject: [928] Re: Repetitive Starts and Stalls on an 84

At 06:26 PM 11/17/01, Mark Reifenberger wrote:
>Due to a number of business trips in a row, my 928 has been parked outside
>with the cover on it for over four weeks now (I always leave one of my
>other cars at the airport parking deck).
>
>This afternoon, I went out to uncover it, start it up and begin using it
>again.  It started right up in about a 1.5 second crank, but then
>immediately died.  It just continues to do this over, and over, and over,
>and over again.  It always starts quickly, but always dies after 2 or 3
>seconds (I'm pleased to find that my battery has plenty of power).
>
>It seems like the fuel pump does not stay running.  It's like I'm getting
>good pressure during the crank, which it starts and runs on for a couple
>of seconds.  But then it's like the pump doesn't know to stay on.
>Regardless of whether I feather the throttle or not, it just goes out.
>
>What device or parameter does the system use to know the engine is running
>and to leave the pump on?  I'm guessing it would be an RPM threshold or
>something.  Any ideas or suggestions for what I should check or look for
>would be very much appreciated.  Please reply direct, as I'm in digest
>mode.


The '84 is the last year of the electronic fuel pump relay. Power for the 
electronics in the relay comes from the ignition bus (15) to terminal 15 in 
the relay socket. Porsche commonly uses a switched ground, rather than 
switched power, as in this case. The signal for the electronics switch 
comes to terminal 31b from terminal O7 (plugs on bottom of main power panel 
are identified A-W left to right, with no I), and thru a green wire from 
terminal 16 on the transistor ignition system.

When power is applied to the relay thru terminal 15, the electronics turns 
the relay on for two seconds or so. If there is no pulsed signal on 
terminal 31b, the electronic will turn the fuel pump off. If there is a 
pulsed signal from the ignition, showing that the engine is running, the 
electronic switch will hold the relay on, allowing the fuel pump to run. 
This is a safety system, designed to remove fuel pressure anytime that the 
engine stops.

First test would be to install a temporary jumper from terminal 30 to 
terminal 87 in the socket for relay XVII, and try to crank the  engine. If 
it now runs normally, check for pulsed power on terminal 31b in the socket. 
If there is pulsed power there, the fuel pump relay may be bad. Try 
reinstalling it to be sure that it isn't just a bad connection.

Wally Plumley
928 Specialists